`wp_unique_term_slug()` appends numeric suffixes when the requested slug is
already in use by a sibling term. Changes introduced in [32837] inadvertently
caused this suffixing to be skipped in cases where the requested slug is
suffixed with the parent slug, so that it became possible to have two terms
`childslug-parentslug` underneath to the same `parentslug`. We fix this
regression by ensuring that the numeric-suffix routine runs in all cases.
Props yashar_hv, saskak, dlh.
Fixes #46431.
git-svn-id: https://develop.svn.wordpress.org/trunk@45893 602fd350-edb4-49c9-b593-d223f7449a82